Hydraulic pump unloading valve



July 4, 1950 L. F. FRASER HYDRAULIC PUMP UNLOADING VALVE Filed Feb. 19, 1945 Patented July 4, 195() UNITED' ATENT (Granted 'under the act of Marchs3; 1883-,"H `as amended'AprilV 30, 1928;?70 O. G; 757)' equally adaptable to` any situationpwhere hydraulically, actuable devices-. operate only intermittently andlorfwhere the. pumpl supplyingA iluid underfrpressure delivers `a greater volume oi' lipid into the system-than is required by. the hydraulicallyA actuablef devices.,

Hydraulic systems of thisrclass usually consist u which the device: is, particularly. useful,y it` is otra, constantfspeed pump-which charges the hydraulic accumulator atngthe pressure desired `for operating the control units, fluid under-.the desiredpressure being; drawn `from the accumulator or from the high sideoi the systemjinto which the accumulator: is connectedat such intervals as the controlfunitsare required .tobe alctuated. Inasmuchras ytirerspeed of the-pump is constant and the deliveryfofiluidqbyjhe pump into ithe system is, in excessqof that requiredin the` operation, and because the demand on Vthe fluid supply isf intermittent, somefmeans is necessarily provided..` for disposing or the` surplus fluid beingdischargedby,the-pump intothe high pressureside of the system;

The manner `in 1 which; the foregoing difficulty is;l ordinarily solved isby provid-ing, the .wellknownv puppet release valvev which is4 spr-ing loaded to keep it onits seat unti1 the maximum system pressure is -reached whereupon'fthefpressure raises ,it and allows the surplus-.fluidito be bypassed backto the low-pressure side. Itis well known, however, that the pump with this arrangement must operateagainst thefulll pressure of the-highpressure sidevat all times.

The disadvantage has created a,.need.for an unloading valve, a device whereby when the maximum system pressure is reached a return valve openswide and connects the discharge side ofthe pump back to the-lo'wfpressure side and coincidentally a checkvalve closes toseparate the dischargesideloi thepumpirom the accumulator which .thereby prevents escape of fluid under pressurev4 fron1 .th e accumulator back,r to the returnv va1ve. whereby, the pump operates against 'substantiallrzero.pressure ,until the` system pressure drops Va., predetermined'arnount and the return iiuid flQWis again stopped by closing ofthe valve. Y

Unloadingv valves as heretofore .gproposednhave been complicated in construction, costly to manufacture and .diflicult tonraintain in proper ad-` justment.

It is therefore anobject offthis invention .to provide a valve o fL a Sort which is sin 1ple,j ei f ec tive,jand at la .comparatively low cost 'and having no parts which require critical adjustment. In a. valve of 'this typeit is a requirement that when the return valve opens to unload the pumpend coincidentally separate the discharge side, of .the pumpn from the accumulator, a, considerable drop in accumulatorpressure shouldtake place before the return valve again closes.

It is therefore another object of this invention to provide means Wh'erebythe overlapbetween the opening ofthe vreturn valve to .unload4 the Dump and ytheclosing ofthe return valve torcistore the pumplto itsactive condition .maybe ac curately controlle d.

Other objects rwill becomeevdent'irom,a, con.- sideration of the followingw description when taken in conjunction Vwith the drawings, wherein, th'e single gure of =the, drawingsschematically shows an improved unloading valve mechanism in longitudinalyertical section connectedin a simple hydraulic system towhichit is applicable.

In the drawinga pump lD ihasasuctiomside l2 connectedtothe supply tank Il l'andits dis.- Icharge side I 6V conlliled to the fluid inlet passageway I8 of my improved unloading valve2. The fluid dischargelassageway 22` ofthe unloading valve is connected by a pipe 24ste an vaccumulator 26; which for purposes of illustration consists of,a cylindrioalhousing, 25,' a. piston 2 7 slidable therein, and a spring 23j urging the piston towal'djthespace 3l Within the cylinder.

The pipe Zfl'continues on pastjthe accumulator extending to one terminal' 2 8 'of a selector valve 3); The main fludreturn passage', 32"isfconnected-by a pipe lif'to the top of thetank lil. Terminal36 'ofthe selector valve Sllis connected by apipe 38"to the pipe 34 andthus back to the tank I4. Opposite ends of an actuator llare connected-by pipes :42' and fill to the terminals 56" and 48; respectively, of'the selector valve.

AA piston 50"is moved'in one or the other directions as :duid entersthe actuator through pipe asiasoq.

42 into the space 43 or through pipe 4'4 into the space 45 depending on which position the plug 52 of the actuator valve occupies at that time. The unloading valve assembly 20 comprises a body valve 54 containing a fluid inlet passageway I8, the uid discharge passageway 22 and the main fluid return passageway 32. A main check valve 56 is kept from its seat 60 by fluid flow, a spring 58 being provided to urge the valve 56 to its closed position.

When the main check valve 56 is open it permits the passage of fluid from the pump through the main chetck valve 56 to the accumulator 26 and to the selector valve 30 but when it is closed prevents fluid flow from the fluid discharge passageway 22 back through the main check Valve 56 to the fluid inlet passageway I8. The return check valve 62 has a stem 64 with a return [check valve actuating piston 66 at its free end, the piston being slidable in a return check valve actuating cylinder 68. Pressure in the fluid inlet passageway I8 holds the return check valve 62 on its seat 10 when the valve is closed. A light spring- 12 also acts against the return check valve actuating piston 66 and urges the return check valve 62 to its closed position when it is open. Fluid under system pressure entering the chamber 14' will open the valve 62 against system pressure tending to close it by reason of the greater effective area of the piston 66 over the effective area on the valve 62. The chamber 'I6 around the spring 12 may be vented to the atmosphere or it may be connected as by an auxiliary return pipe 18 to the larger pipe 'I9 and thereafter back to the tank I4 whereby any leakage past the piston 66 .will be returned to the tank I4'.

Extending through the body 54 are a series of axially aligned bores 80, 82, 84, 85, and 86, which dene chambers 88, 92, 93, and 94. An auxiliary-valve actuating piston 96 is slidable in the bore 80 and is urged toward the left end of its travel bythe spring 98, the tension of which is regulatable by the hollow externally threaded cap |00. A'piston rod |02 is axially adjustable in the piston 96 by the nut |04 and comprises the linkage whereby the auxiliary-valve actuating piston 96 `actuates the two auxiliary valves |06 and II2.v Another auxiliary return pipe |03 connects the chamber |05 which contains the spring 98 back to the tank I4 by Way of the pipe 19.

The passageway |01 joins the vchamber 88 to the fluid discharge passageway 22. The first auxiliary check valve |06 is axially movable in the bore 82 and is normally kept on its seat |08 by pressure in the chamber 88 whereby the chambers 88 and 92 are kept separated. A spring I|0 assists somewhat in keeping the rst auxiliary check valve |06 closed but its principal function is to urge the valve to its closed position when it is open. An internally threaded collar I|3 on a threaded portion on the rod |02 is adjustable to define the position of the auxiliary valve actuating piston 96 at which the first-auxiliary check valve |06 will be opened. A passageway joins the chamber 92 to the chamber 14 above the piston 66. The second auxiliary check valve ||2 is axially movable in the bore 86 and, whether closed or open, is urged to the right toward its seat ||4 by the spring H6, the tension of which is adjustable by the screw H8.

When the second auxiliary check valve ||2 is closed and the first auxiliary check valve |06 is open, full system pressure is applied to the valve- CII ||2 to hold it on its seat. When valve I l2 seats, it separates chambers 93 and 94. The seating of the valve |I2 may be prevented upon contact with the end of the auxiliary valve actuating piston rod I 02 until the piston 96 moves slightly fur-v ther toward the right than the position shown in the drawing. Chamber 03 is connected back to the tank by the pipe 19. A passageway I I9 joins the chamber 94 to the passageway III whereby the chamber 84 is in communication with the chamber 14. The operation of the system shown, which includes an embodiment of my improved unloading valve, is as follows:

Rotation of the pump I0 draws fluid from the tank I4, discharges it into the fluid inlet passageway I8 and forces the main check valve 56 open and delivers the fluid from the fluid discharge passageway 22 through pipe 24 into the accumulator 26 and to the terminal 28 of the selector valve 30. With th-e plug 52 of the selector valve positioned as shown the fluid will flow from the terminal 28 out through the terminal 48 and pipe 44 into the space 45, thereby moving the piston 50 to the left. I'

By turning the plug 52 through one-quarter turn fluid will flow fromthe terminal 28 out through the terminal 46 and pipe v 42 into the space 43, thereby moving the piston 50 to the right. As long as the accumulator is not fully charged to the desired system pressure, the accumulator piston 21 will continue to move downward and compress the spring 29, and coincidentally the auxiliary valve actuating piston 96'will be moved to the right against the resistance of the spring 98. A

When the rising pressure has moved the'accumulator piston 21 down slightly farther than shown in the drawing, the auxiliary valve actuating piston 96 will have moved to the right enough farther than shown to allow the second auxiliary check valve |I2 to rest on its seat ||4, thereby shutting off the chamber 14 from communication with the chamber 93 and therefore from communication with the common auxiliary return pipe 19. At the point where the second auxiliary check valve I|2 has been closed to interrupt the passageways which normally connect the `chamber 94 back to the tank, neither the accumulator piston 21 nor the smaller auxiliary valve actuating piston-96 have yet reached the position of full system pressure.

Thereafter the auxiliary valve actuating piston 96 and the piston rod |02 moves still farther to the right until the adjustable collar I I3 has contacted the rst auxiliary cheok'valve |06 and pushed it from its seat, the collar being so adjusted that the opening of the rst auxiliary check valve |06 occurs just as the desired system pressure is reached. As soon as the rst auxiliary check valve |06 is very slightly opened, the pressure in chamber 88 and 92 will substantially equalize, and thereafter the auxiliary valve actuating piston 96 may be moved to the right more easily than before by fluid which will be transferredback to the chamber 88 by the accumulator 26.

It follows that, once the first auxiliary check valve |06 has broken away from its seat |08, it will move to a relatively wide open position. When this happens the chamber 14 will be connected by passagewayv III, chambers 92 'and 88, and passageway |01 to the fluid discharge passageway 22 whereby the return valve actuating piston 66 will be subjected to full system pressure for opening the return check valve 62 and the 55; second auxiliary checlrrvaive-"I-IZ kvwill be held shut full system pressurefto prevent. escape, offiluid to chamber 93 and back to the tan 1 i f As soon.as.,thefr,eturn .check valve v642 is opened very slightly the pressure in the fluid'inlet passageway: I8 will be below-that in the fluidl discharge passageway. 22,. whereupon the main checkivalveaE-will close. Thereafter the-accumulator rnustiassumeA theburden Vofisupplying `fluid under pressure toV .the chamber 'I4 for opening thereturnichechvalve.S2-widely: l

The accumulator willA therefore continuellto supply `fluid through the firstr auxiliary?. check valve i |06' toa thechamber! "ML2 vuntil the-return chechvvalve-.EZ-is-widefopen; provided, oficours, that the several chambers are so proportioned that the volume of uid drawn from the accumulator to move the return valve actuating piston 6B all the way down, does not permit the auxiliary valve actuating piston i96 to move left more than it moved to the right at the instant thatl the first auxiliary check valve I06 was broken away from its seat, for otherwise the return check valve 62 would not be fully opened.

After the return check valve B2 is thus opened wide to completely unload the pump I0, and the rst auxiliary check valve |06 is again seated, the return check valve will remain wide open until use of fluid by the actuator 40 allows the auxiliary valve actuating piston I96 to move left enough farther to push the second auxiliary check valve I I2 off its seat, whereupon the chamber 'I4 is connected back to the tank I4 and the return check valve actuating piston 66 will be raised iby the spring 'I2 to close the return check valve 62 as shown in the drawing.

It is noted that when the return check valve 62 has been fully opened, and the pump is cornpletely unloaded and the auxiliary check valve actuating piston 9B has moved farther left due to a drop in accumulator pressure, the closing of the first auxiliary check valve |06 ahead of the opening of the second auxiliary check valve I I2, will, in the interim, allow enough leakage of pressure either past the return check valve actuating piston 66 or past the second auxiliary check valve I I2 to reduce the pressure to a point where the spring 198 will not have to push the valve I I2 olf its seat against the full system pressure. It is also noted, that, inasmuch as the leakage past the pistons 6B and '96 may be slight, the chambers 'I6 and |05 may be vented to the atmosphere, and the return pipes 'I8 and |03 omitted.

In the claims the chambers 14, 16, |05, 88, y92, 93 and 84 will be referred to as the rst, second, third, fourth, fth, sixth and seventh chambers respectively.

Having described an embodiment of my invention, I claim:

1. An improved hydraulic unloading valve mechanism which comprises a valve body having a uid inlet passageway and a fluid discharge passageway, a main check valve biased to prevent flow from the fluid discharge passageway back to the fluid inlet passageway, a main fluid return passageway, a return check valve biased to prevent flow from the fluid inlet passageway back to the said main uid return passageway, a return check valve actuating cylinder, a return check valve actuating piston dividing said return check valve actuating cylinder into a rst and a second chamber, an auxiliary check valve actuating cylinder, an auxiliary check valve actuating piston dividing said auxiliary check valve actuating cylinder into a third and a fourth chamber, a1 fifth'k chamber, .airst auxili'arytrlieclrL valve ybiased to `-preventrtllovit` fromv therfourthf. tothe Jfiftli".chamber, af sixth an'daseventh chamber, alfsecond auxiliary "checkl valvegbiasedf:toY prevent' flowfr'om thelseventh-bach to the sixth-chamber, af passageway connecting the fourth chamber. to the vspace between -thef-maini check valve. and I the discharge passageway, af passageway connecting: thefrstl chamber tothe-=fifth andseventhchambers, auxiliary fluidV return passageways extend-v ingifrormth'ev second, third and sixth chambers, and linkage connecting the auxiliary valve-actuating piston" to theV ii'rst and-second auxiliary check valves-,"Vwhereby` movement of isaid .auxiliary valve*actuatingAV piston in response to a predetermined pressure within the fourth chamber opens the said first auxiliary check valve and allows the said second auxiliary check valve to close.

2. The device defined in claim 1 with springs urging the several valves to the closed position.

3. An improved hydraulic unloading valve mechanism which comprises a valve body having a iiuid inlet passageway and a fluid discharge passageway, a main check valve biased to prevent flow from the fluid discharge passageway back to the fluid inlet passageway, a main fluid return passageway, a return check valve biased to prevent ilow from the fluid inlet passageway back to the said main fluid return passageway, a return valve actuating cylinder, a return valve actuating piston dividing said return valve actuating cylinder into a first and a second chamber, an auxiliary valve actuating cylinder, an auxiliary valve actuating piston dividing said auxiliary valve actuating cylinder into a third and a fourth chamber, a fth chamber, a first auxiliary check valve biased to prevent flow from the fourth to the fifth chamber, a sixth and a seventh chamber, a second auxiliary check valve biased to prevent flow from the seventh back to the sixth chamber, a passageway connecting the fourth chamber to the space between the main check valve and the discharge passageway, a passageway connecting the first chamber to the fifth and seventh chambers, an auxiliary fluid return passageway extending from the sixth chamber, means for venting the second and third chambers, and linkage connecting the auxiliary valve actuating piston to the rst and second auxiliary check valve whereby movement of said auxiliary valve actuating piston in response to a predetermined pressure within the fourth chamber opens the said first auxiliary check valve and allows the said second auxiliary check valve to close.

4. An improved hydraulic unloading valve mechanism which comprises a valve body having a fluid inlet passageway and a fluid discharge passageway, a main valve adapted to prevent flow from the fluid discharge passageway back to the fluid inlet passageway, a main fluid return passageway, a return valve adapted to prevent ow from the fluid inlet passageway back to the said main fluid return passageway, a return valve actuating cylinder, a return valve actuating piston dividing said return valve actuating cylinder into a first and a second chamber, an auxiliary valve Iactuating cylinder, an auxiliary valve actuating piston dividing said auxiliary valve actuating cylinder into a third and a fourth chamber, a fth chamber, a first auxiliary valve adapted to prevent ilow from the fourth to the fifth chamber, a sixth and a seventh chamber, a second auxiliary valve adapted to prevent flow from the seventh, back to the .sixth chamber, apassageway connecting thevfourthchamber .to the, space be tween the main .Valve andy the'discharge, passageway,- a passageway connecting the first chamber to the vi-lfth and seventh chambers, an auxiliary 5 uid return passageway extending fromthe sixth chamber, means for ventingthe second and third chambers, and linkage connecting the `auxiliary valve actuating piston to the first vand second auxiliary valves, whereby movement of ,said auxiliaryY valve actuating piston in response to a predetermined pressure Withinthe fourth chamb er opens the s aid rst auxiliary valve` and allows the said second auxiliary valve to close.

LLOYD EERASER. 15 2,342,001v

, `mzrERENQlES 0112121)v le of this patent: Y-

UNITED STATES PATENTS Number NameY Date 726,841 Ball May 5, 1903 2,015,801 -Johnson Oct. 1, 1935 2,214,817 Harrington Sept. 17, 1940, 2,241,665 Herman May 13, 1941 2,264,375 H111 Dec. 2, 1941 2,279,176 Pardee Apr. 7, 1942 2,313,351 Magnuson Mar. 9, 1943 2,316,445 Marshall Apr. 13, 1943 ,1, Magnuson Feb. 15, 1944 

